The invention relates to a pulse-controlled inverter with minimized electromagnetic interference emission.
Although the present invention and the problem on which it is based are explained on the basis of an electric vehicle having a pulse-controlled inverter, they are also applicable to any other electrical drive systems having clocked, electrically powered inverters.
In an electrical drive system of an electric vehicle or a hybrid electric vehicle, a polyphase voltage is usually fed into an electric machine by an inverter, for example in the form of a pulse-controlled inverter. For this purpose, an energy storage device, such as a high-voltage battery, can energize a DC link circuit, which for its part provides a DC voltage that can be converted into a polyphase AC voltage, for example a three-phase AC voltage, in order to feed the electric machine.
To that end, conventional pulse-controlled inverters (PCI) comprise typically at least three fundamental components. On the input side, a DC link capacitor is typically used to couple a DC voltage into the DC link circuit. The DC link capacitor is connected to one or more power modules by means of a low-inductance electrical connection, e.g. in the form of two busbars made of copper. In this case, the busbar that is connected to a first output connection of the DC link circuit can be referred to as high-side busbar and the busbar that is connected to a second output connection of the DC link circuit can be referred to as low-side busbar. In order to generate a three-phase output voltage, a power module is typically embodied with three bridge branches each having two semiconductor switches. Accordingly, the semiconductor switches of the bridge branches that are connected to the high-side busbar are referred to as high-side switches and the semiconductor switches of the bridge branches that are connected to the low-side busbar are referred to as low-side switches, respectively. Examples of semiconductor switches that can be used here are IGBT (insulated-gate bipolar transistor) modules with a diode connected in antiparallel or MOSFETs (metal-oxide-semiconductor field-effect transistors) or the like. The power module usually operates with pulse-width-modulated drive signals for the semiconductor switches in order to generate the polyphase output voltage.
In addition to their desired electrical properties, all three components of a pulse-controlled inverter, i.e. the DC link capacitor, the electrical connection by means of busbars and the power module, have undesired stray variables as well, i.e. stray capacitances and stray inductances. On account of the stray variables, clocking the individual half bridges in the converter generates transient electrical interference variables that can propagate in the system. As a result, these undesired output coupling points can lead, inter alia, to line-based interference emissions in the energizing DC voltage grid of the inverter. However, said line-based interference emissions can be kept as low as possible by virtue of the fact that all of the subcomponents of the system per se are arranged symmetrically between the high side and the low side with regards to the stray variables. One challenge here is, in particular, the symmetrical arrangement of the power modules with regard to their stray variables.
The document Domurat-Line A., Hoene E. “Analysis and Reduction of Radiated EMI of Power Modules”, 7th International Integrated Power Electronics Systems Conference (CIPS), 2012 discloses, for example, power modules that are arranged on the basis of flip-chip technology, in which the low-side switches are soldered on “overhead”. Said flip-chip technology can be readily implemented for prototypes, but series production with large quantities based on commercially available IGBT modules is difficult.
A simpler, alternative design is thus required in order to minimize the line-based interference emissions of clocked, electrically powered inverters.